The invention pertains to optical cross-connect switches. More particularly, the invention pertains to such switches which incorporate modular interconnect fabrics.
Optical switches are known and are useful in implementing optical communications networks using fiberoptic transmission lines. In such networks, it is at times necessary to switch the optical signals between optical transmission paths.
One known type of optical switch is an optical cross-connect switch. In such switches, in a general case, any one of N input lines can be coupled to any one of N output lines.
One known type of cross-connect switch 10 is implementable using the Spanke architecture illustrated in FIG. 1. In a Spanke architecture with N inputs and N outputs, N1xc3x97N switches 12a, b, c, . . . n are connected by an interconnect fabric 16 to N1xc3x97N output switches 18a, b . . . n. 
The interconnect fabric 16 has N2 total static connections. One connection is between each input-output pair of switches. Therefore, an Nxc3x97N fabric has a total of N2 fibers with N2 inputs and N2 outputs.
Insertion loss is a major concern in optical cross-connect switches. Although a single stage Spanke design can achieve small insertion loss, this solution creates yet another problem: namely, the difficulty of creating the large interconnecting fabric because the fabric contains N2 connections.
Methods are known to implement small interconnect fabrics. For example, pre-routed fibers can be sandwiched between flexible plastic sheets sometimes called optical flypapers. They are however very difficult to create for N greater than 32. Alternately, the interconnections can be made from N2 individual fibers. However, this solution is time consuming to build and difficult to maintain.
There thus continues to be a need to be able to cost effectively design and implement larger cross connect switches of various sizes. It would be especially advantageous if it would not be necessary to custom create a different interconnect networks for each switch. Preferably, a known interconnect design can be reliably and cost effectively manufactured and could be used to implement a variety of switches.
A recursive process for creating large signal interconnects from a plurality of smaller, standardized, interconnect modules, which could incorporate individual optical fibers or electrical conductors, produces interconnect systems for specific applications using only standard modular building blocks. In accordance with the method, a first modular Kxc3x97K interconnect network having K2 signal carriers is defined and implemented. For L inputs,   L  K
input groups are formed. For M outputs,   M  K
output groups are defined.
A plurality of   (            L      K        xc3x97          M      K        )
of the first modular interconnects can be used to form an Lxc3x97M passive interconnect network having Lxc3x97M signal carriers.
A plurality of the Lxc3x97M, modular interconnects, all of which are substantially identical, and all of which are based upon multiples of the basic Kxc3x97K modular interconnect can be combined to form a larger Nxc3x97N interconnect. For example, where L=M, and where N is an integer multiple of M,   N  M
input groups and   N  M
output groups result in       (          N      M        )    2
Mxc3x97M modules being needed to implement the Nxc3x97N connectivity. This type of network is especially desirable in that economies of scale in manufacturing, reliability and inventory can be achieved since Nxc3x97N networks for various values of N can be implemented using multiple, identical Kxc3x97K basic building blocks which in turn form the larger Mxc3x97M assemblies which are combined to make the Nxc3x97N networks.
In one embodiment, an Nxc3x97N cross-connect switch incorporates a plurality of substantially identical interconnect modules. A plurality of input switches is coupled to N2 inputs to the modules. A plurality of output switches is coupled to N2 output sides of the modules.
In one aspect, the switches can be divided into groups with one set of groups associated with the input sides of some of the modules and another set of groups associated with the output sides.
In another aspect, a switch requiring N inputs and N outputs can be implemented with multiple identical modules that have K2 inputs and K2 outputs. The number of required modules is (N/K)2. In such configurations, the connectivity between the interconnect, a plurality of 1xc3x97N input switches and a plurality of Nxc3x971 output switches can be implemented using optical ribbon cables. The pluralities of switches each contain N switches.
Interconnect modules can be implemented with optical transmitting fibers. Alternately, they could be implemented with electrical conductors.
A method of implementing an Nxc3x97N cross-connect switch includes establishing a Kxc3x97K modular interconnect where K less than N. Providing       (          N      K        )    2
interconnect modules. Coupling N2 inputs to and receiving N2 outputs from the modules.
In yet another aspect, interconnects, implemented from pluralities of smaller interconnect modules can in turn become modular building blocks for even larger interconnect fabrics. In accordance herewith Mxc3x97M fabrics can be implemented with smaller Nxc3x97N building blocks. In one embodiment, M is an integer multiple of N.
Non-symmetrical switches with N1 inputs and N2 outputs can be implemented using Kxc3x97K interconnect modules where K less than N1 and K less than N2. With   N1  K
input groups and   N2  K
output groups,   (            N1      K        xc3x97          N2      K        )
interconnect modules will be required.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.